Surgically implanted cardiac pacing systems, such as pacemakers and defibrillators, play an important role in the treatment of heart disease. In the 50 years since the first pacemaker was implanted, technology has improved dramatically, and these systems have saved or improved the quality of countless lives. Pacemakers treat slow heart rhythms by increasing the heart rate or by coordinating the heart's contraction for some heart failure patients. Implantable cardioverter-defibrillators stop dangerous rapid heart rhythms by delivering an electric shock.
Cardiac pacing systems typically include a timing device and a lead, which are placed inside the body of a patient. One part of the system is the pulse generator containing electric circuits and a battery, usually placed under the skin on the chest wall beneath the collarbone. To replace the battery, the pulse generator must be changed by a simple surgical procedure every 5 to 10 years. Another part of the system includes the wires, or leads, which run between the pulse generator and the heart. In a pacemaker, these leads allow the device to increase the heart rate by delivering small timed bursts of electric energy to make the heart beat according to a healthy rhythm. In a defibrillator, the lead has special coils to allow the device to deliver a high-energy shock and convert potentially dangerous rapid rhythms (ventricular tachycardia or fibrillation) back to a normal rhythm. Additionally, the leads may transmit information about the heart's electrical activity to the pacemaker.
For both of these functions, leads must be in contact with heart tissue. Most leads pass through a vein under the collarbone that connects to the right side of the heart (right atrium and right ventricle). In some cases, a lead is inserted through a vein and guided into a heart chamber where it is attached with the heart. In other instances, a lead is attached to the outside of the heart. To remain attached to the heart muscle, most leads have a fixation mechanism, such as a small screw and/or hooks at the end.
Within a relatively short time after a lead is implanted into the body, the body's natural healing process forms scar tissue along the lead and possibly at its tip, thereby fastening it even more securely in the patient's body. Leads usually last longer than device batteries, so leads are simply reconnected to each new pulse generator (battery) at the time of replacement. Although leads are designed to be implanted permanently in the body, occasionally these leads must be removed, or extracted. Leads may be removed from patients for numerous reasons, including but not limited to, infections, lead age, and lead malfunction.
Removal or extraction of the lead may be difficult. The body's natural healing process forms scar tissue over and along the lead, and possibly at its tip, thereby encasing at least a portion of the lead and fastening it even more securely in the patient's body. In addition, the lead and/or tissue may become attached to the vasculature wall. Both results may, therefore, increase the difficulty of removing the leads from the patient's vasculature. Typical leads in a human may pass through the innominate vein, past the superior vena cava (“SVC”), and into the right atrium of the heart. Tissue growth occurring along the SVC and other locations along the innominate vein may increase the risk and difficulty in extracting the leads from such locations, particularly when the vein(s)' walls are thin and the surrounding tissue is notably fibrous.
A variety of tools have been developed to make lead extraction safer and more successful. Current lead extraction techniques include mechanical traction, mechanical devices, and laser devices. Extracting a lead may often involve applying tension to the lead while it is still implanted, whether in order to pull it free using the tension force, to loosen it, and/or to apply an extraction device over the lead. Applying an extraction device over a lead which is not adequately tensioned may result in kinking or damage to the lead, for example at locations which are not as easy to access as the proximal portion of the lead that was near to or coupled with the pacemaker or defibrillator. In extracting a lead, the lead (including any conductive portions, insulating sheath, and/or casing layers) is often cut between the distal end of the lead and the proximal end of the lead (which is often coupled to the pacemaker). In other situations, the lead exhibits structural failure, either before, or during, the lead extraction surgical intervention. These situations may result in a lead that is not as long as the clinician would like it to be in order to both apply tension to the lead and/or deploy an extraction device over the lead. Existing lead extension technologies may be limited in the maximum level of tension which they can support in coupling with the lead, with the reversibility of such coupling, and/or with the reliability of such coupling.